Landfills receive large masses of discarded asphalt-based materials. The term “asphalt-based materials” includes for example, roofing shingles and felt; asphalt paving; asphalt-treated wood products such as posts, poles, and landscaping timbers; and tar paper.
Taking shingles as an example, in most cases, these used shingles result from tear-offs prior to reroofing a building. To avoid overloading the building structure, shingles must be torn off after at most three layers have been installed. In other cases, manufacturers or wholesalers discard new shingles with manufacturing defects or that are too old to use.
Whenever shingles are scrapped, they must be disposed of properly. The usual practice now is to pay for their disposal. In some cases this may amount to 10-20% of the total cost of the reroofing project.
Shingles and other asphalt-based materials do however, have a number of constituents which when separated from each other have value. These comprise asphalt, gravel, sand, fine calcium carbonate particles, and binders such as fiberglass, asbestos, or paper. Used shingles also include steel fasteners, typically staples or shingle nails. Discarded asphalt paving has substantial amounts of gravel and sand (aggregate).
Further, some discarded shingles contain asbestos. Safe practice usually requires that the entire mass be treated as hazardous waste requiring expensive disposal. The need to treat large volumes of discarded shingles as hazardous because of a small amount of asbestos contained in them adds expense for the owner of the structure from which such shingles were removed.
The commercial value of the asphalt constituent in asphalt-based materials depends in part on the price of crude oil and in part on the fraction of the material that asphalt comprises. Increased price for crude oil increases the commercial value of the asphalt component of asphalt-based materials as well. Increased value of the asphalt and other constituents means that an efficient, inexpensive process for separating the constituent materials in discarded asphalt-based materials into relatively pure constituent streams becomes economically attractive.
Other processes recycle unused shingles and tear-offs by grinding them. The resulting particles can be used to make recycled asphalt shingles or as a component of road paving material. While this process does divert the shingle mass from landfills, it produces a particle mass having relatively small economic value compared to the value of substantially separated constituents of the shingles.
Processes for recycling other types of discarded asphalt-based materials operate differently, or in some cases, not at all. For example, asphalt paving may be ground and blended into new road pavement material
A process able to separate the constituents of waste asphalt-based materials into nearly pure materials would produce materials having substantial value. These separated materials would be useable for all of the purposes that such materials normally have, including reuse in the manufacture of new asphalt-based materials. In those cases where asbestos is present in the worn asphalt-based materials, concentrating this hazardous material by such a process will reduce the disposal cost.